JP2005321462A - Fixing device, low frictional sheet and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a rubbing member used for a fixing device using a belt member from being worn or deformed. <P>SOLUTION: The fixing device is equipped with a fixing roll 61, an endless belt 62 capable of moving while coming into contact with the fixing roll 61, a pressure pad 64 arranged inside the endless belt 62 and forming a nip part N, and the low frictional sheet 68 provided between the endless belt 62 and the pressure pad 64. The low frictional sheet 68 is constituted of base material 681 composed of fluororesin fiber, and a fluororesin layer 682 laminated at least on the endless belt 62 side of the base material 681, and also constituted so that elongation percentage to tensile load of 0.75N per 1cm width in 200°C atmosphere may be ≤5.0%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device and the like, and more particularly to a fixing device used in an image forming apparatus using an electrophotographic system.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, for example, a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged, and the photosensitive drum is controlled based on image information. An electrostatic latent image is formed on the photosensitive drum by exposure with the exposed light. The electrostatic latent image is converted into a visible image (toner image) with toner, and the toner image is transferred onto the recording paper from the photosensitive drum, and then the toner image is fixed on the recording paper with a fixing device.

  As shown in FIG. 7, the fixing device used in such an image forming apparatus includes a heating source 114 inside a cylindrical metal core 111, a heat-resistant elastic body layer 112 on the metal core 111, and an outer peripheral surface thereof. A fixing roll 110 formed by laminating a release layer 113 on the core, a pressure-contacting arrangement with respect to the fixing roll 110, a heat-resistant elastic body layer 122 on a core metal 121, and a heat-resistant resin film or It comprises a pressure roll 120 formed by laminating a release layer 123 made of a heat resistant rubber coating. Then, the recording paper carrying the unfixed toner image is passed between the fixing roll 110 and the pressure roll 120, and the unfixed toner image is heated and pressed to thereby apply the toner to the recording paper. The image is fixed. Such a fixing device is called a roll nip method and is generally widely used.

By the way, in order to increase the speed of the heating roll type fixing device, it is necessary to increase the nip width in proportion to the fixing speed so that a sufficient amount of heat can be supplied to the toner and the recording paper. As a method of increasing the nip width, there are a method of increasing the load between the fixing roll and the pressure roll, a method of increasing the thickness of the elastic layer, and a method of increasing the roll diameter.
However, in the method of increasing the load or the method of increasing the thickness of the elastic layer, the shape of the nip width due to the deflection of the roll becomes non-uniform along the roll axis. This causes a problem in image quality such as occurrence. In addition, the method of increasing the roll diameter causes problems that the apparatus is increased in size and the time (warm-up time) until the roll is raised from room temperature to a fixable temperature is increased.

  Therefore, in order to solve these problems and realize a fixing device corresponding to the speeding up of the image forming apparatus, the applicant of the present invention has a rotatable fixing roll whose surface is elastically deformed and remains in contact with the fixing roll. An endless belt capable of traveling and a pressure pad arranged in a non-rotating state inside the endless belt, and the endless belt is pressed against the fixing roll so that a contact surface with the fixing roll is formed by the pressure pad. And a belt nip so that the sheet can be passed between the endless belt and the fixing roll, and a fixing device configured to locally elastically deform the exit side of the sheet on the surface of the fixing roll. The technique regarding this is proposed (for example, refer patent document 1).

  In the fixing device described in Patent Document 1 (referred to as “belt nip method”), the endless belt is brought into pressure contact with the fixing roll using a pressure pad instead of the pressure roll in the conventional roll nip type fixing device. By adopting such a configuration, the width of the belt nip formed by the fixing roll and the endless belt can be easily made larger than the width of the conventional roll nip between the fixing roll and the pressure roll. Since a uniform and high nip pressure can be applied to the portion, it is possible to cope with a high speed, and it is easy to reduce the size of the apparatus.

  Furthermore, since the heat capacity of the endless belt pressed against the fixing roll is small, and the pressure pad is arranged in a non-rotating state, a configuration in which heat transmitted from the fixing roll is not easily dissipated to the outside is realized. Therefore, even when the rotation of the fixing roll is started, the amount of heat taken from the fixing roll to the endless belt side is small, the thermal efficiency at the time of melting the toner can be increased, and the amount of temperature decrease at the belt nip is also small. There is also an advantage that the fixing property of the toner can be improved.

Japanese Patent No. 3298354 (pages 4-7)

  By the way, in the fixing device of the belt nip type as described in Patent Document 1 described above, a wide nip can be formed at the nip portion and a uniform and high nip pressure can be applied, but a pressure member (pressure pad) can be used. Since the configuration in which the endless belt is pressed against the fixing roll is adopted, sliding friction occurs between the pressure pad and the endless belt. Therefore, a friction member for reducing sliding friction is disposed on the pressure pad, and a lubricant is applied to the friction surface between the friction member and the endless belt, so that the pressure pad and the endless belt The slidability (slidability) is improved.

However, since the rubbing member rubs against the endless belt under the pressing force between the pressure pad and the fixing roll, the rubbing surface on the endless belt side of the rubbing member is easily worn. When the rubbing surface of the rubbing member wears, the inner peripheral surface of the endless belt is damaged thereby, and the sliding resistance between the rubbing member and the endless belt increases with the worn rubbing member. For this reason, the smooth rotation of the endless belt is hindered, and the recording paper cannot be conveyed well, which may cause image defects such as paper wrinkles and image misalignment.
In addition, the rubbing member may be deformed during long-term use. In that case, the nip pressure becomes non-uniform, and the fixed image may be unevenly fixed. Further, the deformation of the rubbing member increases the sliding resistance between the rubbing member and the endless belt, and causes image defects such as paper wrinkles and image displacement.

  Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to cause wear and deformation in a rubbing member used in a fixing device using a belt member. It is in suppressing.

  For this purpose, the fixing device of the present invention is a fixing device for fixing a toner image carried on a recording material, and includes a rotatable rotating member and a belt movable while contacting the rotating member. A pressure member that is disposed inside the belt member, presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member, and the belt member and the pressure member A rubbing member provided between the substrate and the rubbing member. The rubbing member is composed of a base material made of fluororesin fibers and a fluororesin layer laminated on at least the belt member side of the base material. It is characterized by an elongation rate of 5.0% or less with respect to a tensile load of 0.75 N per 1 cm width in the atmosphere.

Here, the rubbing member can be characterized in that the base material is formed by weaving fluororesin fibers. Further, the rubbing member can be characterized in that it is formed by impregnating a base material with a fluororesin and then firing. Furthermore, the rubbing member can be configured such that irregularities are formed on the surface on the belt member side. Further, the rubbing member may be characterized in that a reinforcing layer made of a heat resistant resin or metal is further laminated on the surface opposite to the belt member.
Further, the belt member may have a configuration in which irregularities are formed on the inner peripheral surface. Furthermore, the heating member which heats a rotation member, or the heating member which heats a belt member can further be provided.

Further, the present invention is regarded as a low friction sheet, and the low friction sheet of the present invention is disposed between a pressure member that presses the belt member against a rotating member facing the belt member, and the belt member. A low-friction sheet having a base material made of fluororesin fibers and a fluororesin layer laminated on at least one surface of the base material, and extending to a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere The rate is 5.0% or less.
Here, the base material may be formed by weaving fluororesin fibers. Moreover, the base material can also be set as the structure formed with the PTFE fiber. Further, the low friction sheet may be formed by impregnating a base material with a fluororesin and then firing. Furthermore, a reinforcing layer made of a heat-resistant resin or metal may be further laminated on one surface of the substrate.

  Further, the present invention is regarded as an image forming apparatus. The image forming apparatus of the present invention includes a toner image forming unit that forms a toner image, and a transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material. A fixing unit that fixes the toner image transferred onto the recording material to the recording material, the fixing unit including a rotatable rotating member, a belt member movable while contacting the rotating member, and a belt A pressure member that is disposed inside the member and presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member; and between the belt member and the pressure member And a rubbing member provided with a base material made of fluororesin fibers and a fluororesin layer laminated on at least the belt member side of the base material, and having a 1 cm width in an atmosphere of 200 ° C. Tensile per hit Is characterized by growth rates for the heavy 0.75N is below 5.0%.

  As an effect of the present invention, by suppressing the occurrence of wear and deformation in the rubbing member used in the fixing device using the belt member, it is possible to suppress the occurrence of paper wrinkles, image displacement, and fixing unevenness over a long period of time. High-quality images can be formed.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in FIG. 1 is an intermediate transfer type image forming apparatus generally called a tandem type, and a plurality of image forming units 1Y, 1M, 1C, and 1K on which toner images of respective color components are formed by electrophotography. The primary transfer unit 10 that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 1Y, 1M, 1C, and 1K to the intermediate transfer belt 15, and the superimposed toner image transferred onto the intermediate transfer belt 15. Are provided with a secondary transfer unit 20 that collectively transfers (secondary transfer) to a paper P that is a recording material (recording paper), and a fixing device 60 that fixes the secondary transferred image onto the paper P. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

  In the present embodiment, each of the image forming units 1Y, 1M, 1C, and 1K has a charger 12 that charges the photosensitive drum 11 around the photosensitive drum 11 that rotates in the direction of arrow A, and the photosensitive drum 11. A laser exposure device 13 for writing an electrostatic latent image thereon (exposure beam is indicated by a symbol Bm in the figure), each color component toner is accommodated, and the electrostatic latent image on the photosensitive drum 11 is visualized with toner. A developing unit 14, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 in the primary transfer unit 10, and a drum cleaner that removes residual toner on the photosensitive drum 11. 17 and the like are sequentially arranged. These image forming units 1Y, 1M, 1C, and 1K are arranged in a substantially straight line from the upstream side of the intermediate transfer belt 15 in the order of yellow (Y), magenta (M), cyan (C), and black (K). Has been.

The intermediate transfer belt 15 as an intermediate transfer member is constituted by a film-like endless belt in which an appropriate amount of an antistatic agent such as carbon black is contained in a resin such as polyimide or polyamide. The volume resistivity is 10 ⁶ to 10 ¹⁴ Ωcm, and the thickness is, for example, about 0.1 mm. The intermediate transfer belt 15 is circulated and driven (rotated) at a predetermined speed in the direction B shown in FIG. 1 by various rolls. As these various rolls, a drive roll 31 that is driven by a motor (not shown) excellent in constant speed and rotates the intermediate transfer belt 15, and an intermediate that extends substantially linearly along the arrangement direction of the photosensitive drums 11. A support roll 32 that supports the transfer belt 15, a tension roll 33 that functions as a correction roll that applies a constant tension to the intermediate transfer belt 15 and prevents meandering of the intermediate transfer belt 15, and a backup provided in the secondary transfer unit 20. A cleaning backup roll 34 provided in a cleaning unit for scraping off residual toner on the roll 25 and the intermediate transfer belt 15 is provided.

The primary transfer unit 10 includes a primary transfer roll 16 that is disposed to face the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween. The primary transfer roll 16 includes a shaft and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR, and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm. The primary transfer roll 16 is placed in pressure contact with the photosensitive drum 11 with the intermediate transfer belt 15 in between, and the primary transfer roll 16 has a voltage (with negative polarity; the same applies hereinafter) having a polarity opposite to that of the toner. (Primary transfer bias) is applied. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15 so as to form superimposed toner images on the intermediate transfer belt 15.

The secondary transfer unit 20 includes a secondary transfer roll 22 disposed on the toner image carrying surface side of the intermediate transfer belt 15 and a backup roll 25. The backup roll 25 is composed of a tube of EPDM and NBR blend rubber with carbon dispersed on the surface, and EPDM rubber on the inside. And it is formed so that the surface resistivity may be 10 ⁷ to 10 ¹⁰ Ω / □, and the hardness is set to 70 ° (Asker C), for example. The backup roll 25 is disposed on the back side of the intermediate transfer belt 15 to form a counter electrode of the secondary transfer roll 22, and a metal power supply roll 26 to which a secondary transfer bias is stably applied is disposed in contact with the backup roll 25. ing.

On the other hand, the secondary transfer roll 22 includes a shaft and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR, and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm. The secondary transfer roll 22 is disposed in pressure contact with the backup roll 25 with the intermediate transfer belt 15 interposed therebetween. Further, the secondary transfer roll 22 is grounded, and a secondary transfer bias is formed between the secondary transfer roll 22 and the backup roll 25. The toner image is secondarily transferred onto the paper P conveyed to the transfer unit 20.

  Further, on the downstream side of the secondary transfer portion 20 of the intermediate transfer belt 15, an intermediate transfer belt that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15. A cleaner 35 is provided so as to be able to contact and separate. On the other hand, on the upstream side of the yellow image forming unit 1Y, a reference sensor (home position sensor) 42 that generates a reference signal serving as a reference for taking image forming timings in the image forming units 1Y, 1M, 1C, and 1K. It is arranged. Further, an image density sensor 43 for adjusting image quality is disposed on the downstream side of the black image forming unit 1K. The reference sensor 42 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. Each image forming unit is instructed by an instruction from the control unit 40 based on the recognition of the reference signal. 1Y, 1M, 1C, and 1K are configured to start image formation.

  Further, in the image forming apparatus according to the present embodiment, as a paper transport system, a paper tray 50 that stores paper P, a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing, and a pickup A transport roll 52 that transports the paper P fed by the roll 51, a transport chute 53 that feeds the paper P transported by the transport roll 52 to the secondary transfer unit 20, and transported after being secondarily transferred by the secondary transfer roll 22. A conveyance belt 55 that conveys the paper P to be fixed to the fixing device 60 and a fixing inlet guide 56 that guides the paper P to the fixing device 60 are provided.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. In the image forming apparatus as shown in FIG. 1, image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is subjected to predetermined image processing by an image processing device (IPS) not shown. After being applied, the image forming operation is executed by the image forming units 1Y, 1M, 1C, and 1K. In IPS, the input reflectance data is subjected to predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and other various image editing. Is done. The image data that has undergone image processing is converted into color material gradation data of four colors, Y, M, C, and K, and is output to the laser exposure unit 13.

  The laser exposure unit 13 irradiates the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, for example, with an exposure beam Bm emitted from a semiconductor laser in accordance with the input color material gradation data. Yes. In each of the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, the surface is charged by the charger 12, and then the surface is scanned and exposed by the laser exposure unit 13 to form an electrostatic latent image. The formed electrostatic latent images are developed as toner images of respective colors Y, M, C, and K by the respective image forming units 1Y, 1M, 1C, and 1K.

  The toner images formed on the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K are transferred onto the intermediate transfer belt 15 in the primary transfer unit 10 where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. Transcribed. More specifically, in the primary transfer portion 10, a voltage (primary transfer bias) having a polarity opposite to the toner charging polarity (minus polarity) is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16, and the toner image. Are sequentially superimposed on the surface of the intermediate transfer belt 15 to perform primary transfer.

  After the toner images are sequentially primary transferred onto the surface of the intermediate transfer belt 15, the intermediate transfer belt 15 moves and the toner image is conveyed to the secondary transfer unit 20. When the toner image is transported to the secondary transfer unit 20, in the paper transport system, the pick-up roll 51 rotates in accordance with the timing at which the toner image is transported to the secondary transfer unit 20, and the paper of a predetermined size is transferred from the paper tray 50. P is supplied. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer unit 20 via the transport chute 53. Before reaching the secondary transfer unit 20, the paper P is temporarily stopped, and a registration roll (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 15 on which the toner image is carried. And the position of the toner image are aligned.

  In the secondary transfer unit 20, the secondary transfer roll 22 is pressed against the backup roll 25 via the intermediate transfer belt 15. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 22. At this time, when a voltage (secondary transfer bias) having the same polarity as the toner charging polarity (negative polarity) is applied from the power supply roll 26, a transfer electric field is formed between the secondary transfer roll 22 and the backup roll 25. Is done. The unfixed toner image carried on the intermediate transfer belt 15 is collectively electrostatically transferred onto the paper P in the secondary transfer unit 20 pressed by the secondary transfer roll 22 and the backup roll 25. .

Thereafter, the sheet P on which the toner image has been electrostatically transferred is transported as it is while being peeled off from the intermediate transfer belt 15 by the secondary transfer roll 22, and transported downstream of the secondary transfer roll 22 in the sheet transport direction. It is conveyed to the belt 55. The conveyance belt 55 conveys the paper P to the fixing device 60 in accordance with the optimum conveyance speed in the fixing device 60. The unfixed toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge placement unit provided in a discharge unit of the image forming apparatus.
On the other hand, after the transfer onto the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and the cleaning backup roll 34 and the intermediate transfer belt cleaner 35 are transferred. Is removed from the intermediate transfer belt 15.

  Next, the fixing device 60 used in the image forming apparatus of the present embodiment will be described. FIG. 2 is a side sectional view showing a configuration of the fixing device 60 of the present embodiment. The fixing device 60 includes a fixing roll 61 as an example of a rotating member, an endless belt 62 as an example of a belt member, and a pressure pad 64 as an example of a pressure member pressed from the fixing roll 61 via the endless belt 62. The main part is composed.

The fixing roll 61 is a cylindrical roll configured by laminating a heat-resistant elastic body layer 612 and a release layer 613 around a metal core (cylindrical cored bar) 611, and is rotatably supported. Rotates at a surface speed of 194 mm / s.
Inside the fixing roll 61, a halogen heater 66 rated at 600 W is disposed as a heat source. On the other hand, a temperature sensor 69 is disposed in contact with the surface of the fixing roll 61. The control unit 40 of the image forming apparatus controls the lighting of the halogen heater 66 based on the temperature measurement value by the temperature sensor 69 so that the surface temperature of the fixing roll 61 maintains a predetermined set temperature (for example, 175 ° C.). It is adjusted to.

The endless belt 62 is an endless belt without a seam, and includes a pressure pad 64 and a belt guide member 63 disposed inside the endless belt 62, and edge guide members 80 ( It is rotatably supported by the latter stage (see FIG. 3). Then, it is arranged so as to be in pressure contact with the fixing roll 61 at the nip portion N, and rotates at a moving speed of 194 mm / s following the fixing roll 61.
Here, FIG. 3 is a configuration diagram illustrating a configuration in which the endless belt 62 is supported, and shows one end region of the fixing device 60 as viewed from the downstream side in the conveyance direction of the paper P.
As shown in FIG. 3, edge guide members 80 are fixed to both ends of the holder 65 disposed inside the endless belt 62. The edge guide member 80 is provided on the outer side of the belt traveling guide portion 801 having a cylindrical shape in which a notch is formed in a portion corresponding to the nip portion N and the vicinity thereof, that is, a C-shaped cross section, A flange portion 802 formed with an outer diameter larger than the outer diameter of the endless belt 62, and a holding portion 803 provided outside the flange portion 802 for positioning and fixing the edge guide member 80 to the fixing device 60 main body. It is configured.

At both ends of the endless belt 62, the inner peripheral surfaces of both ends are supported by the outer peripheral surface of the belt traveling guide portion 801 except for the nip portion N and the vicinity thereof. Rotate along the surface. Accordingly, the belt traveling guide portion 801 is formed of a material having a small friction coefficient so that the endless belt 62 can smoothly rotate, and further has a low thermal conductivity so that it is difficult to remove heat from the endless belt 62. It is made of material.
Further, the flange portion 802 is disposed such that inner surfaces of both flange portions 802 disposed so as to face each other at both end portions of the holder 65 have an interval substantially matching the width of the endless belt 62. When the endless belt 62 rotates, the end of the endless belt 62 abuts against the inner surface of the flange portion 802, so that the movement of the endless belt 62 in the width direction (belt walk) is limited. . As described above, the endless belt 62 is supported by the edge guide member 80 so that the deviation is regulated.

Further, the endless belt 62 is supported by the pressure pad 64 and the belt guide member 63 in the longitudinal region excluding both ends of the endless belt 62 (see also FIG. 2). In the region excluding both ends of the endless belt 62, the inner peripheral surface of the endless belt 62 rotates while sliding on the pressure pad 64 and the belt guide member 63.
The belt guide member 63 is attached to a holder 65 disposed inside the endless belt 62, and is formed of a material having a small friction coefficient so that the endless belt 62 can smoothly rotate. Further, it is preferable that the endless belt 62 is made of a material having low thermal conductivity so that it is difficult to remove heat from the endless belt 62.

Next, the pressure pad 64 is disposed inside the endless belt 62 while being pressed against the fixing roll 61 via the endless belt 62, and forms a nip portion N with the fixing roll 61. In the pressure pad 64, a pre-nip member 64 a for securing a wide nip portion N is disposed on the inlet side (upstream side) of the nip portion N. Further, by locally pressing the surface of the fixing roll 61, the toner image surface is smoothed to give image gloss, and the surface of the fixing roll 61 is distorted (dented) to form a down curl on the paper P. The peeling nip member 64b is disposed on the outlet side (downstream side) of the nip portion N. Further, the pressure pad 64 is provided with a low friction sheet 68 as an example of a rubbing member on the surface in contact with the endless belt 62 in order to reduce the sliding resistance between the inner peripheral surface of the endless belt 62 and the pressure pad 64. It has been.
The pressure pad 64 and the low friction sheet 68 are supported by a metal holder 65.

  The fixing roll 61 is connected to a drive motor (not shown) and rotates in the direction of arrow C. Following this rotation, the endless belt 62 also rotates in the same direction as the fixing roll 61. The sheet P on which the toner image is electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided by the fixing inlet guide 56 and conveyed to the nip N. When the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure acting on the nip portion N and the heat supplied from the fixing roll 61. In the fixing device 60 of the present embodiment, since the nip portion N can be configured widely by the concave pre-nip member 64a that substantially follows the outer peripheral surface of the fixing roll 61, stable fixing performance can be ensured.

  In the vicinity of the downstream side of the nip portion N, the paper P peeled off from the fixing roll 61 by the peeling nip member 64b is completely separated from the fixing roll 61 and guided to a paper discharge path toward the discharge portion of the image forming apparatus. A peeling assisting member 70 is provided. The peeling auxiliary member 70 is held by a baffle holder 72 in a state in which the peeling baffle 71 is close to the fixing roll 61 in a direction (counter direction) opposite to the rotation direction of the fixing roll 61.

Next, each member constituting the fixing device 60 will be described in detail. First, in the fixing roll 61, the core (base material) 611 is formed of a cylindrical body having an outer diameter of 30 mm, a thickness of 1.8 mm, and a length of 360 mm formed of a metal having high thermal conductivity such as iron, aluminum, and SUS. ing.
The heat-resistant elastic body layer 612 is composed of an elastic body having high heat resistance, and it is particularly preferable to use an elastic body such as rubber or elastomer having a rubber hardness of about 15 to 45 ° (JIS-A). Specifically, silicone rubber, fluorine rubber, or the like can be used. In the fixing device 60 of the present embodiment, the core 611 is coated with a silicone HTV rubber having a rubber hardness of 35 ° (JIS-A) with a thickness of 600 μm.

  For the release layer 613, for example, a heat-resistant resin such as a silicone resin or a fluororesin is used, but a fluororesin is suitable from the viewpoint of the releasability to the toner and the wear resistance. As the fluororesin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and the like can be used. The thickness of the release layer 613 is preferably 5 to 30 μm. In the fixing device 60 of the present embodiment, PFA with a thickness of 30 μm is coated and the surface is finished close to a mirror surface state.

The endless belt 62 is a seamless endless belt whose original shape is formed in a cylindrical shape so that a defect due to the seam does not occur in the output image. The base layer and the surface of the base layer on the fixing roll 61 side or It is comprised from the mold release layer coat | covered on both surfaces. The base layer is formed of a polymer such as thermosetting polyimide, thermoplastic polyimide, polyamide, or polyamideimide, and has a thickness of 30 to 200 μm, preferably 50 to 125 μm, and more preferably about 75 to 100 μm. The release layer coated on the surface of the base layer is made of a fluororesin such as PFA, PTFE, or FEP, and has a thickness of about 5 to 100 μm, preferably about 10 to 30 μm.
In the fixing device 60 of the present embodiment, an endless belt 62 having a configuration in which a release layer made of PFA having a thickness of 30 μm is laminated on a base layer made of thermosetting polyimide having a circumferential length of 94 mm, a thickness of 75 μm, and a width of 320 mm. Used.

As described above, the pressure pad 64 disposed inside the endless belt 62 includes the pre-nip member 64a and the peeling nip member 64b, and the holder 65 is configured to press the fixing roll 61 with a load of 35 kgf by a spring or an elastic body. It is supported by. An elastic body such as silicone rubber or fluororubber, a leaf spring, or the like can be used for the prenip member 64 a, and the surface on the fixing roll 61 side is formed with a concave curved surface that substantially follows the outer peripheral surface of the fixing roll 61. In the fixing device 60 of the present embodiment, silicone rubber having a width of 10 mm, a thickness of 5 mm, and a length of 320 mm is used.
The peeling nip member 64b is formed of a heat-resistant resin such as PPS (polyphenylene sulfide), polyimide, polyester, polyamide, or a metal such as iron, aluminum, or SUS. As the shape of the peeling nip member 64b, the outer surface shape in the nip portion N is formed as a convex curved surface having a constant radius of curvature.
In the fixing device 60 of the present embodiment, the endless belt 62 is wrapped around the fixing roll 61 by the pressure pad 64 at a winding angle of about 40 ° to form a nip portion N having a width of about 10 mm.

  Also, the belt guide member 63 disposed in the holder 65 is formed with a plurality of ribs in the rotational direction of the endless belt 62 so as to minimize the contact area with the inner peripheral surface of the endless belt 62. As described above, the belt guide member 63 is made of a material having a low coefficient of friction and low thermal conductivity so that the endless belt 62 does not easily take heat because it rubs against the inner peripheral surface of the endless belt 62. A heat-resistant resin such as PFA or PPS is used.

  Further, the holder 65 is provided with a lubricant application member 67 along the longitudinal direction of the fixing device 60. The lubricant application member 67 is disposed so as to contact the inner peripheral surface of the endless belt 62 and supplies an appropriate amount of lubricant. As a result, the lubricant is supplied to the sliding portion between the endless belt 62 and the low friction sheet 68, and the sliding resistance between the endless belt 62 and the pressure pad 64 via the low friction sheet 68 is further reduced. 62 is smoothly rotated. Further, it has an effect of suppressing wear on the inner peripheral surface of the endless belt 62 and the surface of the low friction sheet 68.

  As the lubricant, a lubricant that has durability against long-term use under a fixing temperature environment and can maintain wettability with the inner peripheral surface of the endless belt 62 is suitable. For example, liquid oil such as silicone oil or fluorine oil, grease in which a solid substance and a liquid are mixed, or a combination thereof can be used. Examples of the silicone oil include dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, carboxy-modified silicone oil, silanol-modified silicone oil, and sulfonic acid-modified silicone oil. In the fixing device 60 of the present embodiment, Methylphenyl silicone oil (KF53: manufactured by Shin-Etsu Chemical Co., Ltd.) is used.

Next, the low friction sheet 68 in the fixing device 60 of the present embodiment will be described.
The low friction sheet 68 is provided between the pressure pad 64 and the inner peripheral surface of the endless belt 62. When the pressing force is applied between the pressure pad 64 and the fixing roll 61 in the nip portion N, the low friction sheet 68 is rubbed against the inner peripheral surface of the endless belt 62, and the endless belt 62 has a function of reducing sliding resistance (friction resistance) between the inner peripheral surface and the pressure pad 64. For this reason, the low friction sheet 68 is required to have a small friction coefficient and excellent characteristics of wear resistance and heat resistance.
Therefore, as shown in FIG. 4 (cross-sectional configuration diagram of the low friction sheet 68), the low friction sheet 68 of the present embodiment is formed by weaving fluororesin fibers such as PTFE fibers by plain weave, twill weave, or the like. The base material 681 and a fluororesin layer 682 made of PTFE or the like coated so as to cover the fluororesin fibers of the base material 681 at least on the inner peripheral surface side of the endless belt 62. At that time, the fluororesin layer 682 covering the fluororesin fiber of the substrate 681 is formed with such a film thickness that the unevenness of the fluororesin fiber appears on the surface. Such a fluororesin layer 682 is formed by impregnating and applying a fluororesin aqueous dispersion to the fluororesin fibers of the base material 681 and firing it. Accordingly, the low friction sheet 68 is formed with unevenness due to the fluororesin fiber on the inner peripheral surface side of the endless belt 62.
Furthermore, the low friction sheet 68 is resistant to the frictional resistance from the inner peripheral surface of the endless belt 62 due to the rotation of the endless belt 62, and from the viewpoint of securing rigidity to maintain the shape as the low friction sheet 68, The elongation for a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere is 5.0% or less.

First, sliding between the endless belt 62 and the pressure pad 64 in the nip portion N will be described.
As described above, the sheet P on which the toner image has been electrostatically transferred passes through the nip portion N of the fixing device 60 to fix the toner image on the sheet P. When the sheet P passes through the nip portion N, The conveying force is received from the fixing roller 61 on the driving side. That is, the paper P is conveyed by receiving a frictional force from the fixing roll 61 as the fixing roll 61 rotates.
On the other hand, in a state where the paper P is not conveyed to the nip portion N, the driven endless belt 62 is also rotated by receiving the frictional force from the fixing roll 61, but the paper P is conveyed to the nip portion N, In a state where the paper P is nipped by the nip portion N, the endless belt 62 receives a conveying force from the fixing roll 61 via the paper P. Accordingly, when viewed from the sheet P side, when the sheet P passes through the nip portion N, the sheet P is subjected to the conveying force from the fixing roll 61 and at the same time, the direction opposite to the conveying direction from the endless belt 62 side. Force (reverse conveying force) is applied.

Therefore, if the sliding resistance between the endless belt 62 and the pressure pad 64 increases, the rotation of the endless belt 62 is not smooth, so that the paper P receives a reverse conveying force from the endless belt 62. It becomes. In that case, the conveyance of the paper P cannot follow the rotation of the fixing roll 61, and slip occurs between the paper P and the fixing roll 61.
In particular, the fixing roll 61 has a so-called flare shape in which the outer diameter increases from the center to both ends, or the pressing force between the peeling nip member 64b and the fixing roll 61 increases from the center to both ends. By setting as described above, in the nip portion N, a force is always applied to the paper P in the width direction from the central portion toward both ends, thereby suppressing the occurrence of paper wrinkles on the paper P. Yes. However, when the sliding resistance between the endless belt 62 and the pressure pad 64 increases and the sheet P cannot follow the conveyance of the fixing roll 61 and slip occurs, the sheet P acts in the width direction of the sheet P. The balance of force will be lost, resulting in paper wrinkles and image misalignment on the paper P.

  Therefore, in the fixing device 60 of the present embodiment, the base material 681 formed by weaving fluororesin fibers on the sliding surface between the endless belt 62 and the pressure pad 64 and at least the inner peripheral surface side of the endless belt 62. , A low friction sheet 68 composed of a fluororesin layer 682 coated so as to cover the fluororesin fibers of the substrate 681 is disposed. Further, the lubricant is supplied to the sliding portion between the low friction sheet 68 and the inner peripheral surface of the endless belt 62 by the rotation of the endless belt 62 whose inner peripheral surface is coated with the lubricant applying member 67. ing. Therefore, the low friction sheet 68 itself is configured with a low coefficient of friction, and further, the lubricant is interposed in the sliding portion between the low friction sheet 68 and the inner peripheral surface of the endless belt 62, thereby The friction coefficient with the inner peripheral surface of the endless belt 62 can be set to be extremely small.

In particular, since the unevenness by the fluororesin fiber is formed on the inner peripheral surface side of the endless belt 62 of the low friction sheet 68, the contact between the low friction sheet 68 and the inner peripheral surface of the endless belt 62 is uneven. As a result, the contact area between the two becomes small. Therefore, the friction coefficient between the low friction sheet 68 and the inner peripheral surface of the endless belt 62 can be further reduced.
Further, since the lubricant can be held in the concave portion of the low friction sheet 68, the lubricant can be supplied from this concave portion to the contact portion (convex portion) between the low friction sheet 68 and the inner peripheral surface of the endless belt 62, The contact portion can always maintain a contact state in which the lubricant is interposed.
In this way, since the sliding resistance between the low friction sheet 68 and the endless belt 62 can be maintained at a low level, the endless belt 62 can be smoothly rotated, and the paper P can be separated from the fixing roll 61. It is possible to stably convey at a constant speed, and it is possible to suppress the occurrence of image misalignment and paper wrinkles.
Further, the wear of the low friction sheet 68 can be suppressed, and even if wear occurs on the rubbing surface of the low friction sheet 68, the exposed base material 681 is made of fluororesin fiber. Can be kept low.

  At that time, in addition to the low friction sheet 68 of the present embodiment, by forming fine irregularities on the inner peripheral surface of the endless belt 62, the retention capacity of the lubricant on the inner peripheral surface of the endless belt 62 is improved. Can be made. By increasing the retention capacity of the lubricant on the inner peripheral surface of the endless belt 62, it is possible to more stably maintain an appropriate amount of lubricant at the sliding portion between the endless belt 62 and the low friction sheet 68. Become. In addition, since the contact area between the endless belt 62 and the low friction sheet 68 can be further reduced, the friction coefficient between the low friction sheet 68 and the inner peripheral surface of the endless belt 62 can be set to be lower.

  By the way, in the low friction sheet 68 of the present embodiment, the fluororesin water dispersion is impregnated and applied to at least the inner peripheral surface side of the endless belt 62 on the fluororesin fiber of the substrate 681 and fired. Thus, a fluororesin layer 682 is formed. Therefore, the fluororesin layer 682 is formed so as to cover the fluororesin fibers of the base material 681 with a uniform film, and is configured so as not to have infiltration and permeability with respect to the lubricant. Thus, since the low friction sheet 68 is formed so as not to be permeable and permeable to the lubricant, the lubricant can be prevented from seeping into the low friction sheet 68. It is not lost and enables stable maintenance of the lubricant. In addition, it is possible to suppress deterioration of the low-friction sheet 68 itself that permeates into the low-friction sheet 68 and maintain heat-resistant stability that can withstand long-term use. Furthermore, it is possible to prevent the lubricant from being deformed by oozing into the pre-nip member 64a of the pressure pad 64 and swelling, thereby changing the nip pressure.

Further, since the fluororesin layer 682 on the surface of the low friction sheet 68 is made of a material having a low affinity with the lubricant (having oil repellency), the lubricant may be excessively held on the surface of the low friction sheet 68. In addition, the fluidity of the lubricant can be increased between the surface of the low friction sheet 68 and the inner peripheral surface of the endless belt 62. For this reason, the lubricant does not stay in the sliding portion, and the replacement with the newly supplied lubricant can be efficiently performed.
Therefore, even if wear powder or the like generated by sliding between the endless belt 62 and the belt guide member 63 enters the sliding portion between the endless belt 62 and the pressure pad 64, the wear powder or the like does not stay. It also has an effect of suppressing an increase in sliding resistance by suppressing an increase in viscosity due to gelation of the lubricant due to. Furthermore, since the time for the lubricant to receive heat at the nip portion N is reduced, thermal deterioration of the lubricant can be suppressed.
If the low friction sheet 68 is arranged on the inner peripheral surface side of the endless belt 62 of the pressure pad 64, the low friction sheet 68 is integrated with the pressure pad 64 even if the low friction sheet 68 is configured separately from the pressure pad 64. Any of these may be used.

Further, in addition to the above-described configuration, the low friction sheet 68 of the present embodiment is configured such that the elongation percentage with respect to a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere is 5.0% or less. The rigidity of the low friction sheet 68 is maintained against the frictional resistance from the inner peripheral surface of the endless belt 62 due to the rotation of the 62.
Here, the tensile properties of the low friction sheet 68 are cut into a rectangular shape having a length of 10 mm and a width of 5 mm in the sliding direction of the low friction sheet 68 using a thermomechanical analyzer TMA-50 (manufactured by Shimadzu Corporation). The sample was measured by determining the amount of elongation at 0.375 N in the process of applying a load up to 0.5 N under an atmospheric temperature of 200 ° C. And this elongation amount was converted per 1 cm width, and it was set as the elongation rate with respect to the tensile load of 0.75N.
Note that the reason for the 200 ° C. atmosphere is that the temperature of the low friction sheet 68 is assumed to be in the nip portion N because the temperature of the low friction sheet 68 is increased to nearly 200 ° C. by the fixing roll 61. It is. Further, the tensile load per 1 cm width is set to 0.75 N. The value that can be generally assumed as the tensile force that the low friction sheet 68 receives from the endless belt 62 due to the sliding between the low friction sheet 68 and the endless belt 62. That's why.

  Thus, the shape as the low friction sheet 68 is maintained by forming the low friction sheet 68 so that the elongation ratio with respect to the tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere is 5.0% or less. Even if the endless belt 62 is rotated and the endless belt 62 is subjected to frictional resistance from the inner peripheral surface of the endless belt 62, the low friction sheet 68 is very little stretched. There is no deformation.

  On the other hand, as shown in the examples and comparative examples in the latter stage (see FIG. 5 in the latter stage), the low friction sheet having an elongation rate of more than 5.0% with respect to a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere. In 68, non-uniform elongation occurs in the longitudinal direction of the low friction sheet 68, and the entire low friction sheet 68 is swelled and wavy. For this reason, the nip pressure at the nip portion N becomes non-uniform in the longitudinal direction, causing non-uniform fixing and image distortion in the fixed image. In addition, the sliding resistance of the endless belt 62 at the nip portion N is partially increased, deteriorating the paper transportability and causing image displacement and paper wrinkles. Furthermore, such an increase in sliding resistance further promotes deformation of the low friction sheet 68.

Here, the low-friction sheet 68 has a rigidity such that the elongation rate with respect to a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere is 5.0% or less, mainly by fluororesin fibers such as PTFE fibers. A base material 681 formed by weaving by plain weave, twill weave, or the like. That is, the elongation percentage is 5.0% or less by variously combining the fiber diameter and weaving method of the fluororesin fibers constituting the base material 681 of the low friction sheet 68 and the fineness of the mesh. High rigidity can be realized.
In addition, the base 681 and the reinforcing layer that reinforces the base 681 can be combined to make the low friction sheet 68 rigid so that the elongation rate is 5.0% or less. For example, even if the base material 681 alone has a structure in which the elongation rate is greater than 5.0%, a film-like heat-resistant resin or metal is laminated as a reinforcing layer on the surface of the low friction sheet 68 on the pressure pad 64 side. By doing so, it is also possible to achieve rigidity such that the elongation rate is 5.0% or less.

Hereinafter, the low friction sheet 68 of the present embodiment will be described in detail based on examples and comparative examples. The low friction sheet 68 of the present embodiment is not limited to the examples.
(Example 1)
A laminate of a stretched PTFE film and a woven fabric made of PTFE fibers (product number # 8181, fiber thickness 400D, satin weave: manufactured by Japan Gore-Tex Co., Ltd.) is used as a base material, and PTFE is applied to the woven fabric surface. A low friction sheet 68 (the woven fabric surface side of the base material is the sliding surface) was obtained by impregnating and applying an aqueous dispersion and firing this. In this case, the low friction sheet 68 has an elongation rate of 4.5% with respect to a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere, and satisfies 5.0% or less.
The low-friction sheet 68 is disposed on the fixing device 60 of the present embodiment so that the woven fabric side of the base material is the endless belt 62 side, and a full-color predetermined color is obtained using a color printer C2220 manufactured by Fuji Xerox Co., Ltd. A running test was performed to output the pattern image on J paper (trade name) manufactured by Fuji Xerox Co., Ltd., and the driving torque of the fixing roller 61 and the image quality of the printed image were evaluated in the initial running and after printing 200,000 sheets. . Here, since the endless belt 62 is configured to follow the fixing roll 61 in the fixing device 60 of the present embodiment, the low friction sheet 68 is measured by measuring a change with time of the driving torque of the fixing roll 61. And the endless belt 62 can be evaluated for sliding resistance.

As a result, the driving torque of the fixing roller 61 is low and stable both at the beginning of running and after printing 200,000 sheets, the sliding resistance between the low friction sheet 68 and the endless belt 62 is kept low, and stable paper conveyance is achieved. The sex was confirmed. In addition, the printed image was free from paper wrinkles, image displacement, and uneven fixing, and the image quality was good.
Further, when the low friction sheet 68 after the running test was visually observed, a slight wavy deformation was found in the low friction sheet 68, but there was no deformation of the pressure pad 64, and as described above, the image quality was improved. There is almost no impact.

(Comparative Example 1)
A low-friction sheet 68 was obtained by impregnating and applying a PTFE aqueous dispersion to a glass cloth substrate and firing it. In this case, the low friction sheet 68 has an elongation rate of 0.3% with respect to a tensile load of 0.75 N per 1 cm width in an atmosphere of 200 ° C. and satisfies 5.0% or less.
Using this low friction sheet 68, a running test similar to that of Example 1 was performed. The driving torque and image quality were good in the initial stage of running, but after printing 200,000 sheets, the driving torque increased. It was confirmed that the sliding resistance between the low friction sheet 68 and the endless belt 62 was increased. In addition, large image shifts and paper wrinkles occurred.
Further, when the low friction sheet 68 after the running test was visually observed, the low friction sheet 68 was not deformed, but the surface fluororesin (PTFE) was worn and the glass fibers were exposed. In this state, the pressure pad 64 was not deformed.

(Comparative Example 2)
A 800 μm thick nonwoven fabric made of PTFE fibers (Polyflon web: manufactured by Daikin Industries, Ltd.) was used as a base material to obtain a low friction sheet 68 as it was. In this case, the low friction sheet 68 has an elongation rate of 12.0% with respect to a tensile load of 0.75 N per 1 cm width in an atmosphere of 200 ° C., and does not satisfy 5.0% or less.
Using this low friction sheet 68, a running test similar to that of Example 1 was performed. The driving torque and image quality were good in the initial stage of running, but an increase in driving torque was observed during the running test. Uneven fixing and paper wrinkles also occurred as a result of the deterioration of paper conveyance at the time of printing 10,000 sheets.
Further, when the low friction sheet 68 after the running test was visually observed, the low friction sheet 68 was found to have a wavy deformation, and deformation due to swelling of the pressure pad 64 was observed.

(Comparative Example 3)
The base used in Comparative Example 2 was impregnated with a PTFE aqueous dispersion and fired to obtain a low friction sheet 68. In this case, the low friction sheet 68 has an elongation rate of 7.0% with respect to a tensile load of 0.75 N per 1 cm width in an atmosphere of 200 ° C., and does not satisfy 5.0% or less.
A running test similar to that of Example 1 was performed using the low friction sheet 68. The driving torque was low and the image quality was good in the initial stage of running, but an increase in driving torque was observed during the running test. At the time of printing 200,000 sheets, uneven conveyance and paper wrinkles also occurred as a result of the deterioration of paper transportability.
Furthermore, when the low friction sheet 68 after the running test was visually observed, the low friction sheet 68 was found to have a wavy deformation, but the pressure pad 64 was not deformed.

(Example 2)
The low friction sheet 68 was obtained by laminating and bonding a 20 μm thick polyimide sheet on the surface opposite to the rubbing surface of the low friction sheet 68 used in Comparative Example 3. In this case, the low friction sheet 68 has an elongation rate of 1.0% with respect to a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere, and satisfies 5.0% or less.
Using this low friction sheet 68, a running test similar to that of Example 1 was performed. As a result, the driving torque was low, the paper transportability was stable, and the image quality was good at the beginning of running and after printing 200,000 sheets. It was.
Further, when the low friction sheet 68 was visually observed after the running test, the low friction sheet 68 was not found to be wavy and the pressure pad 64 was not deformed.

FIG. 5 summarizes the results of the above examples and comparative examples. As shown in FIG. 5, by using the low friction sheet 68 of the present embodiment, it is possible to smoothly rotate the endless belt 62 without causing the low friction sheet 68 to be deformed, such as undulation or undulation. Therefore, it is possible to suppress the occurrence of image defects such as paper wrinkles, image displacement, and fixing unevenness.
The effect of the low friction sheet 68 of this embodiment is clear by comparison with the comparative example.

As described above, the low friction sheet 68 disposed in the fixing device 60 of the present embodiment includes the base material 681 formed by weaving fluororesin fibers by plain weave, twill weave, or the like, and at least the endless belt 62. It is comprised with the fluororesin layer 682 coat | covered so that the fluororesin fiber of the base material 681 may be covered in the inner peripheral surface side, and the elongation rate with respect to the tensile load 0.75N per 1 cm width in 200 degreeC atmosphere is 5.0% It is formed as follows.
With this configuration, the friction coefficient between the low friction sheet 68 and the inner peripheral surface of the endless belt 62 can be set low. In addition, it is possible to suppress the occurrence of deformation such as undulation or undulation in the low friction sheet 68. For this reason, the nip pressure at the nip portion N becomes non-uniform over the longitudinal direction, causing the fixing image to be unevenly fixed or disturbing the image, and the sliding resistance of the endless belt 62 at the nip portion N to be partially increased. Since the smooth rotation of the endless belt 62 can be suppressed, good paper transportability can be maintained, and the occurrence of paper wrinkles and image misalignment can be suppressed.

[Embodiment 2]
In the first embodiment, an image forming apparatus in which a fixing roll using a fixing roll as a heating unit and an endless belt with a pressure pad pressed as a pressing unit is mounted has been described. In the second embodiment, a fixing device mounted on the image forming apparatus shown in FIG. 1, which uses an endless belt with a heat generation source pressed as a heating unit and uses a pressure roll as a pressing unit. explain. In addition, about the structure similar to Embodiment 1, the same code | symbol is used and the detailed description is abbreviate | omitted here.

FIG. 6 is a side sectional view showing a configuration of the fixing device 90 in the present embodiment. As shown in FIG. 6, in the fixing device 90 of the present embodiment, the fixing belt 92 is disposed on the toner image carrying surface side of the paper P. A ceramic heater 82 which is a resistance heating element as a heat source is disposed inside the fixing belt 92, and heat is supplied from the ceramic heater 82 to the nip portion N.
The ceramic heater 82 has a substantially flat surface on the pressure roll 91 side. Then, it is arranged in a state of being pressed against the pressure roll 91 via the fixing belt 92 and forms a nip portion N. Therefore, the ceramic heater 82 also functions as a pressure member. The sheet P that has passed through the nip portion N is peeled off from the fixing belt 92 by the change in the curvature of the fixing belt 92 in the exit region (peeling nip portion) of the nip portion N.
Further, in order to reduce the sliding resistance between the inner peripheral surface of the fixing belt 92 and the ceramic heater 82 between the inner peripheral surface of the fixing belt 92 and the ceramic heater 82, a low friction sheet 68 as an example of a rubbing member. Is arranged. The low friction sheet 68 may be configured separately from the ceramic heater 82 or may be configured integrally with the ceramic heater 82.

On the other hand, a pressure roll 91 as an example of a rotating member is disposed so as to face the fixing belt 92 and is rotated in the direction of arrow D by a drive motor (not shown), and the fixing belt 92 is driven to rotate by this rotation. Has been. The pressure roll 91 includes a core (cylindrical cored bar) 911, a heat-resistant elastic body layer 912 coated on the outer peripheral surface of the core 911, and a release layer 913 made of a heat-resistant resin coating or a heat-resistant rubber coating. Has been configured.
The fixing belt 92 is an endless belt whose original shape is formed in a cylindrical shape. The base layer 921 is formed of a heat-resistant resin such as polyimide, polyamide, or polyamideimide, or a metal such as SUS or nickel, and the base layer. A release layer 922 made of a fluororesin or the like coated on the surface or both surfaces of the pressure roll 91 of 921.
Further, in the vicinity of the downstream side of the nip portion N, a peeling auxiliary member for completely separating the paper P peeled from the fixing belt 92 from the fixing belt 92 and guiding it to a paper discharge path toward the discharge portion of the image forming apparatus. 70 is disposed. The peeling auxiliary member 70 is held by a baffle holder 72 in a state where the peeling baffle 71 is close to the fixing belt 92 in a direction (counter direction) opposite to the rotation direction of the fixing belt 92.

  The paper P on which the toner image has been electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided to the nip N of the fixing device 90 by the fixing inlet guide 56. When the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure acting on the nip portion N and the heat supplied from the ceramic heater 82 on the fixing belt 92 side. Also in the fixing device 90 of the present embodiment, since the nip portion N can be configured widely between the pressure roll 91 and the ceramic heater 82, stable fixing performance can be ensured.

Here, also in the fixing device 90 of the present embodiment, the low friction sheet 68 includes the base material 681 formed by weaving fluororesin fibers by plain weave, twill weave, or the like, and at least on the inner peripheral surface side of the fixing belt 92. It is composed of a fluororesin layer 682 coated so as to cover the fluororesin fibers of the substrate 681, and is formed with an elongation rate of 5.0% or less with respect to a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere. ing.
With this configuration, the friction coefficient between the low friction sheet 68 and the inner peripheral surface of the fixing belt 92 can be set low. In addition, it is possible to suppress the occurrence of deformation such as undulation or undulation in the low friction sheet 68. For this reason, the nip pressure at the nip portion N is not uniform over the longitudinal direction, causing the fixing image to be unevenly fixed or disturbing the image, and the sliding resistance of the fixing belt 92 at the nip portion N to be partially increased. Further, since it is possible to suppress hindering the smooth rotation of the fixing belt 92, it is possible to maintain good paper transportability, and it is also possible to suppress the occurrence of paper wrinkles and image misalignment.

  As an application example of the present invention, application to an image forming apparatus such as a copying machine or a printer using an electrophotographic method, for example, application to a fixing apparatus that fixes an unfixed toner image carried on a recording paper (paper). is there. Further, there is application to an image forming apparatus such as a copying machine or a printer using an ink jet method, for example, a fixing device that dries an undried ink image carried on a recording paper (paper).

1 is a schematic configuration diagram showing an image forming apparatus of the present invention. 2 is a side cross-sectional view illustrating a configuration of a fixing device according to Embodiment 1. FIG. It is a block diagram explaining the structure by which an endless belt is supported. It is a section lineblock diagram of a low friction sheet. It is the figure which showed the evaluation result regarding a low friction sheet. FIG. 4 is a side cross-sectional view illustrating a configuration of a fixing device according to a second embodiment. FIG. 10 is a side sectional view showing a configuration of a conventional fixing device.

Explanation of symbols

1Y, 1M, 1C, 1K ... image forming unit, 11 ... photosensitive drum, 12 ... charger, 13 ... laser exposure device, 14 ... developer, 15 ... intermediate transfer belt, 16 ... primary transfer roll, 17 ... drum cleaner , 20 ... Secondary transfer section, 60, 90 ... Fixing device, 61 ... Fixing roll, 62 ... Endless belt, 63 ... Belt guide member, 64 ... Pressure pad, 64a ... Pre-nip member, 64b ... Peeling nip member, 65 ... Holder , 66 ... Halogen heater, 67 ... Lubricant application member, 68 ... Low friction sheet, 681 ... Base material, 682 ... Fluorine resin layer, 69 ... Temperature sensor, 70 ... Peeling auxiliary member, 82 ... Ceramic heater, 91 ... Pressurization Roll, 92 ... fixing belt

Claims (13)

A fixing device for fixing a toner image carried on a recording material,
A pivotable pivot member;
A belt member movable while contacting the rotating member;
A pressure member that is disposed inside the belt member and that presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member;
A rubbing member provided between the belt member and the pressure member,
The rubbing member is composed of a base material made of fluororesin fibers and a fluororesin layer laminated on at least the belt member side of the base material, and has a tensile load of 0. A fixing device having an elongation ratio with respect to 75N of 5.0% or less.   The fixing device according to claim 1, wherein the rubbing member is formed by braiding a fluororesin fiber on the base material.   The fixing device according to claim 1, wherein the rubbing member is formed by impregnating the base material with a fluororesin and then firing.   The fixing device according to claim 1, wherein the rubbing member has irregularities formed on a surface on the belt member side.   The fixing device according to claim 1, wherein the rubbing member further includes a reinforcing layer made of a heat-resistant resin or metal on a surface opposite to the belt member.   The fixing device according to claim 1, wherein the belt member has irregularities formed on an inner peripheral surface thereof.   The fixing device according to claim 1, further comprising a heating member that heats the rotating member or a heating member that heats the belt member. A pressure member that presses the belt member against a rotating member facing the belt member, and a low friction sheet disposed between the belt member,
A base material made of fluororesin fibers;
A fluororesin layer laminated on at least one surface of the substrate;
A low friction sheet characterized by having an elongation rate of 5.0% or less with respect to a tensile load of 0.75 N per 1 cm width in a 200 ° C. atmosphere.   The low friction sheet according to claim 8, wherein the base material is formed by weaving fluororesin fibers.   The low friction sheet according to claim 8, wherein the base material is formed of PTFE fiber.   The low friction sheet according to claim 8, wherein the low friction sheet is formed by impregnating the base material with a fluororesin and then firing.   9. The low friction sheet according to claim 8, wherein a reinforcing layer made of a heat resistant resin or metal is further laminated on one surface of the substrate. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material,
The fixing means is
A pivotable pivot member;
A belt member movable while contacting the rotating member;
A pressure member that is disposed inside the belt member and that presses the belt member against the rotating member to form a nip portion through which the recording material passes between the rotating member and the belt member;
A rubbing member provided between the belt member and the pressure member,
The rubbing member is composed of a base material made of fluororesin fibers and a fluororesin layer laminated on at least the belt member side of the base material, and has a tensile load of 0. An image forming apparatus characterized in that an elongation ratio relative to 75N is 5.0% or less.

Images